Various domestic network standards have recently become available for the networking of appliances in the domestic area.
A consortium of companies, in particular companies in the computer industry, led by Microsoft, have started an initiative for the specification of a network control software based on the existing Internet Protocol (IP). This network system has become known by the abbreviation UPnP (Universal Plug and Play). In this system, the specification does not relate primarily to entertainment electronic appliances and, in fact, other appliances can also be integrated in the network, in particular personal computers, domestic appliances in the white goods range, such as refrigerators, microwave cookers, washing machines, as well as heating controllers, lighting controllers, alarm systems and so on.
A working group of the UPnP forum have worked out the UPnP-AV specification, which builds on the general UPnP specification and extends it, for application of the UPnP method to AV appliances. In order to transfer AV data (audio/video data) in a domestic network such as this between a so-called server (source appliance) and a so-called renderer appliance (destination appliance), the UPnP-AV specification stipulates that known transmission protocols should be used for transportation of the data. The so-called HTTP-GET method (HTTP stands for Hyper Text Transfer Protocol) and, in addition, the so-called RTP method (RTP stands for Real Time Transport Protocol) are mentioned as known protocols in the specification. These two transport mechanisms are available when the network subscriber stations are linked to one another via Ethernet bus connections.
The HTTP-GET method is based on the TCP method (Transmission Control Protocol), which is a basic connection-oriented transport protocol, in which protected data transmission (with error correction) takes place. The TCP method is in turn built on the Internet Protocol (IP). The HTTP-GET method was developed especially for the transmission of files (for example HTML web pages) from a web server to a web browser. In consequence, it is not adapted for real-time data transmission in sections, for example as occurs on transmitting audio or video data streams. On the other hand, the HTTP-GET method is widely used and is designed to be very simple for the application programmer, so that it is widely popular.
The transport mechanism according to the RTP method is based on the UDP method (User Datagram Protocol), which is likewise built on the Internet Protocol, operates without any connection and does not use error correction, so that disturbances may occur when data is transmitted using this method. On the other hand, the RTP method is better suited to real-time data transmissions, because it uses intermediate buffers, additional time stamps and sequence numbers. In this respect, it is thus more suitable for transmission of audio or video information, particularly on the Internet, which is characterized by numerous bottlenecks.
The transport mechanism based on the HTTP-GET method is recommended for the transmission of AV data streams in the UPnP specification. The HTTP-GET method was intended primarily for requesting a resource which is available in the network, which in many cases is an existing file, and then to transmit this entirely in one piece to the destination appliances. In addition, the so-called chunked transfer encoding method was introduced in HTTP Version 1.1, as well, and this is intended to be used whenever a resource is to be transmitted whose overall length is not yet entirely known at the time when the transmission starts. In this case, the resource should be transmitted in sections but continuously (that is to say without any gaps).